1. Field of the Invention
The present invention relates to a mono-component toner for developing an electrostatic latent image by electrophotographic, electrostatic recording, and electrostatic printing methods, and developing method for same.
2. Description of the Related Art
Development of electrostatic latent images by electrophotographic, electrostatic recording, and electrostatic printing methods is accomplished by electrostatically adhering triboelectrically charged toner to an electrostatic latent image formed on the surface of a photosensitive member so as to render said latent image visible.
Two-component developing method using a two-component developer comprising a magnetic carrier and a toner, and mono-component developing method using mono-component developer comprising a toner without a carrier are well-known as electrostatic latent image developing methods of the aforesaid types.
Magnetic mono-component toners which contain magnetic particles and non-magnetic mono component toners which do not contain magnetic particles are well known as toners used in mono-component developing methods.
Mono-component developers are more difficult to attain a specific toner charge than are two-component developers.
In two-component developers, for example, mixing which charges the toner by mixing the toner and carrier at suitable times to attain stable charge by adequately assuring contact and circulation of the toner and carrier.
In mono-component developers, on the other hand, a toner regulating member is arranged so as to make contact with a developing sleeve, and the mono-component toner is triboelectrically charged by passing between said toner regulating member and said developing sleeve, and the charged toner is maintained on the surface of the developing sleeve by electrostatic force so as to be transported to a developing region to develop an electrostatic latent image formed on the surface of a latent image-bearing member. Uniform charging of the toner to a specific charge amount is difficult inasmuch as the charge attained by the momentary passage between the developing sleeve and the toner regulating member cannot be assured. When the toner charge is low, not only is the amount of the toner charge reduced, but reverse charged toner may result with the result that toner adheres to the non-image portion of the latent image-bearing member, thereby causing fogging of the obtained image. Conversely, when the toner charge is excessive, toner is electrostatically retained on the developing sleeve, thereby reducing image density due to the reduced amount of toner particles adhering to the latent image, and further reducing transfer efficiency due to the increased electrostatic force relative to the latent image-bearing member. These disadvantages are particularly serious in the case of producing ever finer toner particles in response to demands for increased image quality, and in the case of triboelectric charging of toner under high temperature and high humidity conditions.
In the previously mentioned mono-component developing devices, toner is subjected to mechanical stress when it passes between the toner regulating member and the developing sleeve. Thus, a disadvantage arises inasmuch as toner readily tends to become anchored to the toner regulating member. When toner becomes anchored to the toner regulating member, less toner is transported to the developing region which is observable as white streaks on the developing sleeve. This type of toner retention irregular distribution of the toner on the developing sleeve, and causes inadequate charging by the toner regulating member.
Although toner toughness or heat resistance can be improved to prevent the aforesaid toner retention and anchoring, simply improving toughness on heat resistance leads to offset by the heating roller, and reduced fixing hardness.
An example of a mono-component developing device is disclosed in U.S. patent application Ser. No. 5,189,476 pertaining to a developing device provided with a developing sleeve including whiskers. The developing sleeve provided with whiskers in the aforesaid disclosure has excellent wear resistance, toner transportability, and toner chargeability. Particularly when a small size non-magnetic mono-component toner is used in a developing method using the aforesaid developing sleeve, the charge rise becomes unstable, and a high load is exerted by the whiskers on the toner, such that image density is reduced and transfer efficiency is reduced until a saturation charge is attained.